Sportsboard Stiffening System

ABSTRACT

The invention relates generally to sports boards, and more particularly to a reinforcing stiffening system for surfboards. The stiffening system comprises fibrous profiles adhered on the top surface and/or bottom surface of the surfboard foam core. The invention relates in particular to a surfboard equipped with the present stiffening system for preventing board breaking, whereas the surfboard exhibits high stiffness, flex recovery and fracture resistance, and thus enhancing safety for surfboard riders. The fibrous profiles may have a round cross-section. The foam core is encapsulated by a top laminated foam skin at a foam core top surface, and the foam core is encapsulated by an inner bottom foam layer and an outer bottom foam layer on a foam core bottom surface.

FIELD OF THE INVENTION

This invention relates generally to sportsboards, and more particularly to surfboards equipped with a stiffening system having a plurality of fibrous profiles.

BACKGROUND OF THE INVENTION

Surfboards are recreational sporting goods used for surfing in the ocean. Surfboards are typically used in a stand up position during surfing. Therefore surfboard structures are necessary reinforced to achieve high stiffness and break resistance. In general, surfboard structures can be divided into two main categories according to surfboard structures and production technology: fiberglass surfboards and non-fiberglass surfboards.

A typical type one fiberglass surfboard manufacture utilizes a light density foam blank encased on both the deck surface and bottom surface with a hard coating of fiberglass cloth and resin. This type of surfboard has a hard surface and is usually referred as hard surfboard. Typical foam materials include expanded polystyrene foam (EPS) and polyurethane foam (PU). The foam blank can be incorporated stringer system for controlling flex and reinforcing strength of entire surfboard. Typically a centerline stringer, formed of balsa wood, is sandwiched between two halves of foam blank. Other stiffening materials suitable for stringers may include metal tubes, fiberglass tubes and carbon fiber tubes. In general, the design of reinforcing stringer tubes has a cross-section of round shape or other hollow profile shapes for the purpose of weight reduction.

A cross-sectional view of a typical hard surfboard reinforced by fiberglass layers is illustrated in FIG. 1. The reinforcing stringer 1 is typically a rectangular cross-section wood strip. The deck skin and the bottom skin are both a layer of conventional fiberglass fabric and epoxy resin coating, forming a structure of hard shell on the outer surfaces of the surfboard. Carbon fiber or other high strength synthetic fibers may be use to replace fiberglass for more light weight and high strength surfboards. Both the top edge and bottom edge of the wood stringer are connected to the resin coating of the top surface and bottom surface of the surfboard. Hard surfboards made by the fiberglass fabric and epoxy resin method requires a labor intensive process and results in high cost.

Type two non-fiberglass surfboards usually do not utilize any resin impregnated fibers in the layered structure. Typically, this type of surfboard comprises a bottom non-foam plastic plate and a deck foam skin. The surfboards have a soft foam skin on the deck and therefore are usually referred to as soft surfboards. These types of surfboards are usually not reinforced by any hard coating of fiberglass resin on the outer surface. Therefore the strength of this type of surfboard depends very much on the stiffness of stringer system within the foam core. As a result, the stringer of a soft surfboard is usually made into a bow shape to conform to the profile of a surfboard having an upturning front section and an upturning tail section.

Stringer materials for soft surfboards are usually selected from resin laminated bamboo board, plywood board and timber board and these boards are cut to the shape of stringers. Unlike the hard surfboard, wood stringer of soft surfboard cannot extend to the bottom surface or the top surface of the foam core. The top skin and bottom skin are laminated layered structures of flexible foam sheets which are prompted to permanent deformation by collapse of foam cells under prolonged compression force against the hard surface of wood stringer. As a result, wood stringers of soft surfboard are usually encapsulated by the foam core and therefore the height of wood stringers in the vertical direction is limited by the thickness of surfboard foam core. Therefore it is desirable to provide soft surfboards with stringer system of higher flexural strength which is not limited by the thickness of surfboard foam core.

The impact from large waves can cause board breaking problems. Such impacts will trigger the stringer to deform in both the vertical direction and the lateral direction. If the impact forces are strong enough and exceed the breaking strength of the wood stringer either in the vertical direction or the lateral direction, the surfboard fails by fracture and may pose a hazard to the user. The fracture problem is caused by the lower flexural strength of stringers made from plywood board, timber board and resin laminated bamboo board compared to fibrous materials. An optimum stringer system balances strength and weight. The flexural strength of a stringer can be effectively improved to avoid board fracture if, for example, the thickness (horizontal direction) of the stringer is increased. However such a change will considerably increase the weight of stringer and is not favorable for a surfboard application. It is desirable to provide surfboards with improved stiffness and break resistant property to enhance durability of the boards particularly in harsh wave conditions. There is a need for an improved stringer system which greatly increases the stiffness and breaking strength of surfboard while at the same time not significantly increasing the cost or complexity of manufacturing such a surfboard.

High performance surfboards are required to flex a desired amount and quickly return to its original position. Such characteristic is usually referred as flex recovery or memory of surfboard. Conventional hard surfboards generally have a hard shell of fiberglass resin coating as the stiffening structure. The advantage of the hard shell construction is its high stiffness and light weight. However surfboards equipped with hard fiberglass shell may be undesirable in the flex patterns because it has too little flex. In addition, hard surfboard can cause injury to riders and therefore only suitable for experience riders. Therefore it is desirable to develop a high stiffness and light weight surfboard comparable to the conventional hard surfboard. At the same time, the surfboard does not have a hard shell construction like soft surfboard, and thus enhancing safety use for surfboard riders.

It is desirable to provide a soft surfboard having different flexure and stiffness characteristics over selected predetermined regions of the board, which ultimately enhances maneuverability and performance of the board to the rider.

Soft surfboards are originally designed for beginner users. However there are demands for performance soft surfboards designed for more experienced surfers. These performance soft boards demand high stiffness and lighter in weight. Performance soft boards in most cases have a thinner foam core than conventional soft surfboards. It is therefore desirable to provide a soft surfboard with a light weight and high strength stiffening system in a thin foam core.

Wood stringers have an inherent problem of high water absorption, leading to degradation and breakage of the stringers. During surfboard usage, there are opportunities of water invasion from the fin holes seeping into the core of foam blank. The water invasion results in degradation and breakage of the stringers. Therefore, there is a need for a stiffening system for soft surfboard and the materials of such stiffening system is resistant to water absorption.

SUMMARY OF THE INVENTION

The invention relates generally to sports board for surfing in ocean such as a surfboard and body board. This present invention seeks to solve the above problems by providing a break resistant composite strengthening system for surfboard. The surfboard stiffening system exhibits higher stiffness and flex recovery and therefore the surfboard is more fracture resistant, greatly enhancing safety for surfboard riders.

The present invention provides a break resistant stiffening system for surfboard comprising: a foam core, a plurality of fibrous profiles evenly distributed on the top surface and/or bottom surface of the foam core, the fibrous profiles are completely or partially embedded inside the foam core wherein the fibrous profiles are bonded with the foam core; an adhesive layer located between the fibrous profiles and the foam core and creating bond between the fibrous profiles and the foam core. The fibrous profiles are substantially aligned along the longitudinal axis of the surfboard and extend substantially the length of the foam core. Reinforced fibrous strips may be applied to increase the bonding area between the fibrous profiles and the foam core so that the fibrous profiles are situated between the fibrous strip and the foam core.

Preferably, the fibrous profiles extend to the two upturning ends of the surfboard foam core and adhere thereon. Preferably, the fibrous profiles are bonded with the foam core via an adhesive layer. Preferably, the fibrous strips are bonded with the foam core via an adhesive layer. Preferably, the fibrous profile has a diameter in the range of 1 mm to 4 mm. Preferably, the adhesive is an epoxy resin.

Compared to conventional soft surfboards, the present invention has the following advantages:

-   -   1. The fibrous rods adhered on the top surface and/or bottom         surface of the surfboard foam core are relatively small and         therefore flexible, allowing the profiles to bend and extend to         the two ends of the surfboard foam core and provide structural         strength to the entire body from the nose to the tail of         surfboard. The fibrous rods provide reinforcement to stiffen the         foam board. Nevertheless the fibrous rods are light weight.     -   2. The tensile strength of fibrous rod is high. When the fibrous         rods are bonded to the foam core as a unified body, the fibrous         rods can greatly inhibit the deformation of the surfboard in the         vertical direction. The fiberglass rods intrinsically has high         elastic properties and can deform under the forces applied by         the user without casing the collapse of the core material, and         can return to its original position while restoring a major         portion of the stored energy of bending. As a result, the         surfboard equipped with the fibrous rods exhibits high stiffness         and flex recovery properties.     -   3. The fibrous profiles preferably have a cross-section of round         shape and can withstand high flexural deformation without         breaking. The combination of multiple fibrous profiles on the         top and bottom of foam core exhibits surprising high flexural         strength against external bending force. When the fibrous         profiles are bonded to the surfboard foam core as a unified         body, the fibrous profiles can greatly inhibit the deformation         of the surfboard both in the vertical direction and transverse         direction. As a result, the stiffening system of the fibrous         profiles increases the breaking strength of the surfboard.     -   4. The fibrous profiles are formed from synthetic fibrous         materials. Unlike conventional wood stringers, the fibrous         profiles do not absorb water and therefore will not be         deteriorated by water invasion to the foam core. The fibrous         profiles are preferably fiberglass fibers set in an epoxy resin.

A sports board stiffening system includes a foam core having a foam core top surface and a foam core bottom surface. The foam core receives fibrous profiles as either lower fibrous profiles or upper fibrous profiles. Lower fibrous profiles can be connected to the foam core bottom surface and a bottom laminated foam skin can cover the lower fibrous profiles. The lower fibrous profiles are preferably adhered to the bottom surface of the foam core, so that the lower fibrous profiles are adhesively bonded to the foam core. The fibrous profiles are preferably formed from synthetic fibrous materials, namely monofilament fiberglass.

The fibrous profiles may have a round cross-section. The foam core is encapsulated by a top laminated foam skin at a foam core top surface, and the foam core is encapsulated by an inner bottom foam layer and an outer bottom foam layer on a foam core bottom surface. The fibrous profiles are formed as high stiffness fiberglass profiles and low stiffness fiberglass profiles. The high stiffness fiberglass profiles have a higher stiffness than the low stiffness fiberglass profiles.

Upper fibrous profiles are molded to the foam core top surface. A top laminated foam skin can cover the upper fibrous profiles. The sports board stiffening system also has foam core grooves receiving the fibrous profiles at a surface to the foam core.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional fiberglass hard surfboard, taken generally along the transverse direction of the surfboard.

FIG. 2 is a perspective view of a conventional surfboard.

FIG. 3 is a perspective view of a conventional body board.

FIG. 4 is a top plan view of a first preferred embodiment of the stiffening system in a surfboard foam core.

FIG. 5 is a partial cross-sectional view of the first preferred embodiment of the stiffening system, taken generally along the transverse direction of the surfboard foam core.

FIG. 6 is a top plan view and a bottom plan view of a first preferred embodiment of the stiffening system in a body board foam core.

FIG. 7 is a partial cross-sectional view of the first preferred embodiment of the stiffening system, taken generally along the transverse direction of the body board foam core.

FIG. 8 is a top plan view of another embodiment of the stiffening system in a body board foam core.

FIG. 9 is a top plan view of a second preferred embodiment of the stiffening system in a surfboard foam core.

FIG. 10 is a partial cross-sectional view of the second preferred embodiment of the stiffening system, taken generally along the transverse direction of the surfboard foam core.

FIG. 11 is an exploded perspective view of the third preferred embodiment of the stiffening system in a surfboard foam core.

FIG. 12 is a cross-sectional view of the third preferred embodiment of the stiffening system, taken generally along the longitudinal direction of the surfboard foam core.

FIG. 13 is a cross-sectional view of the third preferred embodiment of the stiffening system, taken generally along the transverse direction of the surfboard foam core.

FIG. 14 is a cross-sectional view of the preferred embodiment of a surfboard equipped with the first embodiment of the stiffening system, taken generally along the transverse direction of the surfboard.

FIG. 15 is a cross-sectional view of the preferred embodiment of a body board equipped with the first embodiment of the stiffening system, taken generally along the transverse direction of the body board.

The following call out list of elements can be a useful guide in referencing the element numbers of the drawings.

-   10 stiffening system -   11 fibrous profile -   12 foam core top surface -   13 foam core bottom surface -   14 low stiffness fiberglass profiles -   15 high stiffness fiberglass profiles -   16 foam core groove -   17 fibrous profile adhesive coating -   18 side rail surface -   21 foam core -   22 top laminated foam skin -   23 non foamed plastic plate -   24 inner bottom foam layer -   25 outer bottom foam layer -   26 lower rail foam skin -   28 upper rail surface -   29 lower rail surface -   30 surfboard -   31 surfboard front end -   32 surfboard rear end -   33 body board -   34 body board front end -   35 body board rear end -   36 binding strip -   37 stringer plate -   38 stringer plate notches -   41 prior art foam core -   42 prior art upper skin -   43 prior art lower skin -   44 prior art stringer

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Glossary

-   -   Sportsboard: a board used for sports, such as surfboards, sail         boards, windsurf boards, wakeboards, wake skates, body boards         and snow boards.     -   Fibrous profile: a fibrous elongated member having a         cross-sectional profile.     -   Fibrous rod: a rod made of fiber material and a resin having a         cross-sectional profile that can be in a variety of different         shapes.     -   EPS: expanded polystyrene foam     -   PE: polyethylene     -   PO: polyolefin     -   PP: polypropylene     -   EVA: ethyl vinyl acetate     -   EPO: expanded polyolefin     -   EPE: expanded polyethylene     -   PU: polyurethane     -   EPP: expanded polypropylene foam

The invention relates in particular to a surfboard equipped with the present stiffening system 10 for preventing board breaking, whereas the surfboard exhibits high stiffness, flex recovery and fracture resistance, and thus enhancing safety for surfboard riders. The surfboard 30 has a surfboard front end 31 and a surfboard rear end 32. In a prior art surfboard, the prior art stringer 54 is a vertically oriented strip that bisects the prior art foam core 51. The prior art upper skin 52 and the prior art lower skin 53 encapsulate the prior art foam core 51. In the present invention, there is no need for a prior art stringer 54, although one could be included for design purposes. Analogously, the present invention can be used for making a body board 33 including a body board nose at the body board front end 34 and a body board tail at the body board rear end 35.

In the preferred first embodiment shown in FIGS. 4 and 5, the stiffening system 10 comprises fibrous profiles 11 adhered on both the foam core top surface 12 and the foam core bottom surface 13 of the surfboard foam core 21. A foam core groove 16 formed on the surface of the foam core 21 can receive the fibrous profiles 11. The foam core groove 16 is preferably deep enough to allow the fibrous profile 11 to be encapsulated within the foam core. A typical foam core suitable for the present invention is made of expanded polystyrene foam (EPS). In the preferred embodiment, the fibrous profiles are completely or partially embedded inside the foam core such as in foam core grooves 16. The grooves can be cut as slots with a blade to create an incision. The foam core grooves 16 can receive a fibrous profile adhesive coating 17 such as a glue. In an alternative embodiment, the fibrous profiles may be bonded to the surface of the foam core. In another embodiment, a backing layer may be first laminated to the foam core and the fibrous profiles are then bonded to the surface of the backing layer.

In an alternative embodiment, the fibrous profiles may be adhered only on the top surface of the foam core. In another alternative third embodiment, the fibrous profiles may be adhered only on the bottom surface of the foam core. Various modifications can be made without departing from the spirit and scope of the invention. For example, the fibrous profiles may be adhered on any desirable position of the stringer body and additional number of fibrous profiles may be applied to the foam core according to the requirement of mechanical properties. For example, the foam core upper rail surface 28 and the foam core lower rail surface 29 can receive fibrous profiles as well.

The fibrous profile has a cross-section of round shape, rectangle, parallelogram, triangle or any other profile shape, more preferable a round cross-section. As illustrated in FIG. 2, a typical surfboard 30 has an upturning front end 31 and an upturning tail end 32, which are commonly called the nose rocker and tail rocker of a surfboard. To facilitate the strengthening effect, the fibrous profiles and the foam core have to be securely bonded together as a unified body. The fibrous profiles should be relatively thin and possess the characteristics of good flexibility. The fibrous profiles are flexible and therefore allow the profiles to maintain intimate contact with the curved surfaces at the two ends of the foam core. The fibrous profile has small cross-sectional area and therefore light weight. The present invention facilitates the production of light weight fiberglass stiffening system with improved stiffness and break resistance at relatively low material and labor cost. As shown in FIGS. 6 and 7, the first preferred embodiment can also be applied to a body board for stiffening the board.

The fibrous profiles and foam core may be bonded by adhesive, screws, rivets, or other mechanical fasteners. Preferred bonding method is using adhesive. The adhesive used for bonding the fibrous profiles should exhibit high bond strength and good toughness to tolerate the flex of stiffening system induced by the high impact force of ocean wave. Good heat resistance is also important in the application of surfboards because they are exposed directly to sunlight.

In the preferred embodiment, an adhesive coating 17 is applied between the fibrous profiles 11 and the foam core 21. Heat resistant adhesives suitable for the present application include epoxy base adhesives, polyester base adhesives, hot melt adhesives and rubber based adhesives. Epoxy base adhesives are more preferable because they have the characteristics of high bond strength, good toughness and heat resistance.

In the preferred embodiment, the fibrous profile has a cross-section of round shape and is made of fiberglass resin at a diameter in the range of 1 mm to 8 mm and more preferable in the range of 1 mm to 4 mm. When the fibrous profile has an elongated shape, the fibrous profile can be in the shape of a rod. The strength of the reinforced surfboard foam core is mainly contributed by the fibrous profiles. The application of fibrous profiles on the top and bottom surfaces of the surfboard foam core increases the flexural strength of the surfboard in both the vertical direction and the transverse direction and therefore significantly increase the breaking strength of the surfboard. The fibrous profiles can be interwoven to provide a net shaped structure from the individual strands of the fibrous profile.

The fibrous profiles applied to surfboard foam core in the present invention have a sectional thickness generally larger than the thickness of the fiberglass resin coating layer of the conventional hard surfboard. Therefore fibrous profiles exhibit higher elasticity in response to bending. When the surfboard foam core is equipped with stiffening system of fibrous profiles substantially along the entire length of foam core, the stiffening system has greatly improved its flex recovery characteristics. As the fibrous profiles are securely bonded to the foam core, the fibrous profiles function like a spring to evenly distribute any impact force from waves. When the surfboard flex under bending force, the deformation has a stretching effect to the fibrous profiles. The fibrous profiles tend to resist the stretching action from the bending force due to its high tensile strength. The result is that the surfboard has less flex and spring back more quickly under impact force. Consequently, the reinforced surfboard is less prone to breaking, enhancing the safety of the surfboard. In addition, surfboard with improved flex recovery is desirable for enhancing maneuverability and performance of the board to the rider.

Fibrous profiles are formed from synthetic fibrous materials, selected from fiberglass, carbon fiber, other synthetic fibrous materials or mixtures thereof. Alternatively, the stiffness of the stiffening system can be adjusted to the predetermined desired flex value by employing fibrous profiles having different strength. For example, a carbon fiber rod has greater stiffening effect to the composite stringer than a fiberglass rod. The flexural strength of the fibrous rod may be further adjusted by altering the mixing ratio of carbon fiber and glass fiber inside the fibrous rod. For example, a fibrous rod with increased volume percentage of carbon fiber filaments than glass fiber filaments will produce a rod with higher flexural strength. Fibrous rods made from strands of monofilament fibers provide the maximum stiffness compared with fibrous rods made from woven fibers.

The fibrous profiles are preferably formed as fibrous rods. The fibrous rods of the present stringer system are preferably made from strands of fiberglass monofilament because fiberglass rods have high stiffness and yet relative low cost. The fibrous rods made of fiberglass can be made of fiberglass strand mat that is rolled up and infused with a matrix such as an epoxy resin. The fibrous rods can also be made by spinning multi-filament fiberglass strands into a woven cord or rope and then setting with an epoxy resin.

For requirement of higher flexural strength of the stiffening system, the fibrous profiles may have a larger cross-sectional area at the same profile shape or the fibrous profiles have a cross-section shape designed to have higher flexural strength in the vertical direction.

A typical body board for surfing in ocean is shown in FIG. 3. To effect a turn or maneuver a body board, a rider will grasp one corner of nose and lean in the direction of the turn. The rider will bend the forward portion of the board to raise the nose relative to the rest of the board. The action tends to increase drag on the body board bottom and help prevent the nose from burying in the water. To maximize maneuverability by providing a predetermined, bendable or flexible region in the portion of the board adjacent the nose, the board structure has relatively less stiffness in a front portion of the board, adjacent the front end, and relatively greater stiffness in a second portion of the board extending generally rearwardly from the front portion. As a consequence, the front portion of the board has greater flexibility and bendability relative to the second portion of the board. It is another object of the invention to provide a body board with enhanced maneuverability for turning the board in surfing having the characteristics of a relatively flexible front portion and a relatively stiff middle to rear portions of the board.

In particular the invention provides a variable flexure body board in which one portion of the length of the board, constituting approximately the rear two-thirds of the board, is stiff relative to the nose of the board. The variation in the flexure characteristics of the board is provided by a combination of stiffening fiberglass rods. As shown in FIG. 8, fiberglass rods with larger diameter and thus higher stiffness are selectively placed in the rear two-thirds of the board. In contrast, fiberglass rods with smaller diameter are only applied to the front portion of the board for selectively providing greater flexibility in the front portion of the board adjacent the nose. In another embodiment, the fiberglass rods with smaller diameter may extend from the tail portion to the nose portion of the board. The object of the placement and combination of fiberglass rods is to provide a body board with enhanced maneuverability for turning the board in surfing having the characteristics of a relatively flexible front portion and a relatively stiff middle to rear portions of the board. Therefore, low stiffness fiberglass profiles 14 can be installed between high stiffness fiberglass profiles 15. Also, the high stiffness fiberglass profiles 15 can be installed between the low stiffness fiberglass profiles 14. The high stiffness fiberglass profiles 15 can be placed in a rear portion of the body board and the low stiffness fiberglass profiles 14 can be placed in the front portion of the body board.

In another second preferred embodiment of the stiffening system shown in FIGS. 9 and 10, additional binding measure is applied to increase the bonding area and binding force between the fibrous profiles and the foam core of a surfboard. The binding strip layer 36 is applied in such a way that the fiberglass rods are situated between the fiberglass strip and the EPS foam core. The binding strip 36 may be made of a resin impregnated fibrous strip material or a plastic mesh. More preferably, the binding strip is a resin impregnated fiberglass strip. As illustrated in FIG. 9, the fiberglass strips are bonded to the foam core surface substantially in the transverse direction surrounding the foam core. Alternatively the binding strips 36 may be bonded to the foam core surface immediately on top of the fiberglass rods and the binding strips align substantially in the longitudinal direction of the foam core. Alternatively binding strips 36 may be bonded to the foam core at an angle to the longitudinal direction of the foam core. The width of the binding strip 36 can be adjusted if desirable to achieve the required binding force. For example the binding strip 36 may be altered into thin fiber filaments or strands for weight reduction. Furthermore, additional layer may be laminated or applied on the outer surface of the binding strips 36 to promote bonding between the binding strips 36 and the covering foam skins. More preferably, a layer of adhesive material is applied on the outer surface of the fiberglass strips.

In another third embodiment of the stiffening system as illustrated in FIGS. 11, 12 and 13, where fibrous profiles 11 are connected to stringer plates 37 at regular intervals and form a skeleton structure like a hull. The stiffness of the resulting stiffening structure is significantly increased because the stringer plates 37 impose constraint to the deformation of the fibrous profiles. The entire skeleton structure is then bonded to the foam core to form a stiffened composite foam core for a surfboard. The stringer plates 37 can have stringer plate notches 38 for receiving and connecting to the fibrous profiles 11.

During manufacture of the stiffening system, the fibrous profile 11 is made at a diameter in the range of 1 mm to 8 mm and more preferable in the range of 1 mm to 4 mm. The stringer plate 37 has a thickness in the range of 1 mm to 8 mm and more preferable in the range of 1 mm to 4 mm.

Unlike a wood stringer of a soft surfboard, the fiberglass rods of the present invention do not absorb any water and the strength of stiffening system will not be affected by water invasion. Furthermore, the application of the present fibrous profile stiffening system to a soft surfboard foam core will not form a hard surface layer on the foam core. Consequently, the resulting soft surfboard will be safer to user when the surfboard accidentally hits the rider, in particular for beginner surfers.

As shown in FIGS. 2, and 14, the present invention discloses a break resistant surfboard 30, equipped with the composite stiffening system. The surfboard 30 comprises: a foam core 21, fibrous profiles 11 evenly distributed on the surface of the foam core 21, a top laminated foam skin 22 covering the top surface 12 and side rail surface 18 of the foam core 21, whereas the top laminated foam skin 22 comprising at least one layer of expanded foam, a bottom laminated foam skin covering the bottom surface 13 of the foam core 21, whereas the bottom laminated foam skin comprising at least one layer of expanded foam and a non-foaming plastic plate 23 laminated to the outer surface of the bottom foam skin.

The bottom laminated foam skin includes a plurality of expanded foam layers. In general, the densities of the expanded foam layers increases from inside layer to outside layer for enhancing strength of the bottom structure of surfboard. The preferred embodiment shown in FIG. 14 includes a bottom laminated foam skin formed by two layers of expanded foam. The two layers of expanded foam are respectively the inner bottom foam layer 24 which laminated to the bottom surface 13 of the foam core 21 and the outer bottom foam layer 25 which laminated to the bottom surface of the inner bottom foam layer 24.

In the preferred embodiment, the foam core has a thickness between 13 mm and 150 mm and preferably a thickness between 25 m and 90 mm. The foam core has a density between 15 kg/m³ and 65 kg/m³ and preferably a density between 18 kg/m³ and 40 kg/m³. Suitable materials for use as foam core include expanded polystyrene foam (EPS), expanded polypropylene foam (EPP), expanded polyethylene foam (EPE), expanded polyolefin (EPO) and polyurethane foam (PU)., whereas polystyrene foam is the preferred foam core material in the present embodiment. The top laminated foam skin has a thickness between 1 mm and 6 mm and preferably a thickness between 3 mm and 5 mm. The top laminated foam skin has a density between 45 kg/m³ and 176 kg/m³ and preferably a density between 56 kg/m³ and 128 kg/m³. Suitable materials for use as top laminated foam skin include polyethylene foam sheet (PE), polypropylene foam sheet (PP) and ethylene vinyl acetate copolymer foam sheet (EVA), whereas polyethylene foam sheet (PE) is the preferred top foam skin in the present embodiment. The bottom laminated foam skin has a thickness between 1 mm and 6 mm and preferably a thickness between 2 mm and 4 mm. The bottom laminated foam skin has a density between 27 kg/m³ and 128 kg/m³ and preferably a thickness between 38 kg/m³ and 104 kg/m³. Suitable materials for use as bottom laminated foam skin include polyethylene foam sheet (PE), polypropylene foam sheet (PP) and ethylene vinyl acetate copolymer foam sheet (EVA), whereas Polyethylene foam sheet (PE) is the preferred bottom foam skin in the present embodiment. The plastic plate 23 has a thickness between 0.1 mm and 2 mm and preferably a thickness between 0.35 mm and 1.2 mm. Preferred materials for use as plastic plate 23 include polyethylene and polypropylene.

As shown in FIGS. 3, and 15, the present invention discloses a body board 33, equipped with the stiffening system. The body board 33 comprises: a foam core 21, fibrous profiles 11 evenly distributed on the surface of the foam core 21, a top laminated foam skin 22 covering the top surface 26 and the upper rail surface 28 of the foam core 21, whereas the top laminated foam skin 22 comprising at least one layer of expanded foam, a lower rail foam skin 26 covering the lower rail surface 29, a bottom laminated foam skin covering the bottom surface 13 of the foam core 21, whereas the bottom laminated foam skin comprising at least one layer of expanded foam 25 and a non-foaming plastic plate 23 laminated to the outer surface of the bottom foam skin.

In the preferred embodiment, the foam core has a thickness between 15 mm and 75 mm and preferably a thickness between 25 m and 55 mm. The foam core has a density between 15 kg/m³ and 65 kg/m³ and preferably a density between 18 kg/m³ and 40 kg/m³. Suitable materials for use as foam core include expanded polystyrene foam (EPS), expanded polypropylene foam (EPP), expanded polyethylene foam (EPE), expanded polyolefin (EPO) and polyurethane foam (PU), whereas polystyrene foam is the preferred foam core material in the present embodiment. The top laminated foam skin has a thickness between 2 mm and 8 mm and preferably a thickness between 3 mm and 5 mm. The top laminated foam skin has a density between 45 kg/m³ and 176 kg/m³ and preferably a density between 56 kg/m³ and 128 kg/m³. Suitable materials for use as top laminated foam skin include polyethylene foam sheet (PE), polypropylene foam sheet (PP) and ethylene vinyl acetate copolymer foam sheet (EVA), whereas polyethylene foam sheet (PE) is the preferred top foam skin in the present embodiment. The lower rail foam skin is of the same structure and composition as the top foam skin. The bottom laminated foam skin has a thickness between 1 mm and 6 mm and preferably a thickness between 2 mm and 4 mm. The bottom laminated foam skin has a density between 27 kg/m³ and 128 kg/m³ and preferably a thickness between 38 kg/m³ and 104 kg/m³. Suitable materials for use as bottom laminated foam skin include polyethylene foam sheet (PE), polypropylene foam sheet (PP) and ethylene vinyl acetate copolymer foam sheet (EVA), whereas Polyethylene foam sheet (PE) is the preferred bottom foam skin in the present embodiment. The plastic plate has a thickness between 0.1 mm and 1 mm and preferably a thickness between 0.35 mm and 0.55 mm. Preferred materials for use as plastic plate include polyethylene and polypropylene.

Fibrous profiles are formed from synthetic fibrous materials, selected from fiberglass, carbon fiber, other synthetic fibrous materials or mixtures thereof.

The method of making the first preferred embodiment includes the steps of coating a layer of adhesive material on the fibrous profiles; routing a plurality of groove on the surface of foam core; inserting the adhesive coated fibrous profiles into the grooves. After the adhesive coating has completely cured and hardened, the assembled foam core can be used for normal skin laminating process. The additional binding strip of the second preferred embodiment is bonded to the foam core through the similar steps of coating a layer of adhesive material on the binding strip and routing a groove on the surface of foam core. Alternatively the grooves for receiving the fibrous profiles can also be formed by molding of the foam core.

The method of making the third preferred embodiment as shown in FIGS. 11 and 12 includes the steps of coating a layer of adhesive material on the fiberglass rods; inserting the coated fiberglass rods into the notches 38 of the stringer plates 37. The stringer plates are preferably made of plywood or similar materials with high stiffness. Additional mechanical fastening devices may be applied to fasten the fiberglass rods to the plywood plates; the assembled composite stringer system is placed inside the foam core mold. After the EPS foam beads are injected into the mold cavity of the surfboard core, superheated steam is passed into the mold cavity to expand the foam beads. In the heating process, the foam beads are expanded to form the foam core and the heat creates a bond between the fiberglass rods and the foam core via the adhesive coating. Then the assembled foam core as illustrated in FIG. 12 with the stiffening skeleton structure encapsulated inside the EPS foam core can be used for normal skin laminating process.

The fiberglass rods are small and the center of the cross-section of the fiberglass rods are very close to the foam core surface. The foam core surface is supported by the tensile strength and loading of the fibrous profiles which restrict the bending of the surfboard. The foam core is restricted in bending by the tension of the fiberglass rods.

While the particular embodiments of the invention have been illustrated and described above, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. For example, it would be within the scope of the invention to combine the technical features between the various embodiments. Accordingly, it is not intended that the invention be limited by such variations, modifications and improvements. 

1. A sports board stiffening system comprising: a. a foam core having a foam core top surface and a foam core bottom surface; b. a plurality of fibrous profiles completely or partially embedded inside the foam core wherein the fibrous profiles are bonded with the foam core at a location near the foam core surface; c. stringer plates, wherein the stringer plates have a flat planar shape and are vertically oriented in a transverse direction, wherein the fibrous profiles are connected to the stringer plates at intervals to form a skeleton like structure; d. an adhesive layer located between the fibrous profiles and the foam core and creating bond between the fibrous profiles and the foam core; and e. a bottom laminated foam skin covering lower fibrous profiles.
 2. A sports board stiffening system of claim 1, further comprising: a. grooves formed on the foam core, wherein the fibrous profiles are lower fibrous profiles installed to a foam core bottom surface by inserting the fibrous profiles into the grooves; b. stringer plate notches formed on the stringer plates, wherein the fibrous profiles are connected to the stringer plates at the stringer plate notches; and c. a bottom laminated foam skin covering the lower fibrous profiles.
 3. The sports board stiffening system of claim 2, wherein the lower fibrous profiles are adhered to the surface of the foam core, whereas the lower fibrous profiles are adhesively bonded to the foam core.
 4. The sports board stiffening system of claim 2, wherein the fibrous profiles are formed from monofilament fiberglass.
 5. The sports board stiffening system of claim 2, wherein the fibrous profiles have a round cross-section.
 6. The sports board stiffening system of claim 2, wherein the foam core is encapsulated by a top laminated foam skin at a foam core top surface, and wherein the foam core is encapsulated by an inner bottom foam layer and an outer bottom foam layer on a foam core bottom surface.
 7. The sports board stiffening system of claim 2, wherein the fibrous profiles are formed as a first group of fiberglass profiles and a second group of fiberglass profiles, wherein the a first group of fiberglass profiles have a higher stiffness than the second group of fiberglass profiles.
 8. The sports board stiffening system of claim 7, further comprising: d. upper fibrous profiles molded to the foam core top surface; and e. a top laminated foam skin covering the upper fibrous profiles.
 9. The sports board stiffening system of claim 7, wherein the lower fibrous profiles are adhered to the bottom surface of the foam core, whereas the lower fibrous profiles are adhesively bonded to the foam core.
 10. The sports board stiffening system of claim 7, wherein the fibrous profiles are formed from monofilament fiberglass.
 11. The sports board stiffening system of claim 7, wherein the fibrous profiles have a round cross-section.
 12. The sports board stiffening system of claim 7, wherein the foam core is encapsulated by a top laminated foam skin at a foam core top surface, and wherein the foam core is encapsulated by an inner bottom foam layer and an outer bottom foam layer on a foam core bottom surface.
 13. The sports board stiffening system of claim 7, wherein the fibrous profiles are formed as a first group of fiberglass profiles and a second group of fiberglass profiles, wherein the a first group of fiberglass profiles have a higher stiffness than the second group of fiberglass profiles.
 14. The sports board stiffening system of claim 13, wherein the lower fibrous profiles are adhered to the surface of the foam core, whereas the lower fibrous profiles are adhesively bonded to the foam core.
 15. The sports board stiffening system of claim 13, wherein the fibrous profiles are formed from monofilament fiberglass.
 16. The sports board stiffening system of claim 13, wherein the fibrous profiles have a round cross-section.
 17. The sports board stiffening system of claim 13, wherein the foam core is encapsulated by a top laminated foam skin at a foam core top surface, and wherein the foam core is encapsulated by an inner bottom foam layer and an outer bottom foam layer on a foam core bottom surface.
 18. The sports board stiffening system of claim 17, wherein the fibrous profiles are formed as a first group of fiberglass profiles and a second group of fiberglass profiles, wherein the a first group of fiberglass profiles have a higher stiffness than the second group of fiberglass profiles.
 19. The sports board stiffening system of claim 13, further comprising: foam core grooves receiving the fibrous profiles at a surface of the foam core, wherein the grooves are deep enough to encapsulate the fibrous profiles.
 20. The sports board stiffening system of claim 13, further comprising: foam core grooves receiving the fibrous profiles at a surface of the foam core, wherein the grooves are not deep enough to completely encapsulate the fibrous profiles. 